We shall investigate the properties and functions of testicular somatic cells in the seminiferous tubules, the nature of their responses to follicle stimulating hormone and testosterone at different stages of development, and elucidation of those properties of Sertoli cells and peritubular myoid cells utilized to create a unique microchemical environment in the adluminal compartment which is required for germinal cell development in mammals. We shall analyze the surface components of germinal cells which seem likely to play a role in their recognition by Sertoli cells at different stages of germinal cell development. We shall analyze some of the components produced by Sertoli cells and secreted into the adluminal compartment. We shall use primary cultures of testicular somatic cells prepared from testes at varying stages of sexual maturation and cultured under defined conditions in the presence and absence of various modulators.